1. Field of the Invention
The present invention relates to a vehicle network system and a method of controlling states of vehicle apparatuses in which plural slave apparatuses and a master are connected to a transmission path, and the master sends commands through the transmission path to control states of the slave apparatuses.
The present application is based on Japanese Patent Application No. Hei. 10-184752, which is incorporated herein by reference.
2. Description of the Related Art
A vehicle network system of the type is mounted on a vehicle, and includes slave apparatuses including electric apparatuses such as a radio, an amplifier, a compact disc player (hereinafter, referred to as “CD player”), and a compact cassette player; and a master apparatus including an audio/video controller (hereinafter, referred to as “A/V controller”) and the like. The slave apparatuses and the master are connected to a transmission path such as a common bus.
In the above vehicle network system, the master transmits an operation request command to the slave apparatuses through the transmission path, thereby controlling the states of the slave apparatuses. Therefore, the slave apparatuses start to operate in response to the operation request command.
When the state of one of the slave apparatuses is changed, for example, when the CD player is transferred from the stop state to the play state, the slave apparatus transmits the state change as a state report, to the master. The master monitors the state report sent from the slave apparatus.
In such a network system, when an abnormality such as a transmission error, an abnormal operation of one of the slave apparatuses, or a runaway of a slave apparatus which is not controlled by the master is developed, the network system enters an abnormal condition.
In order to prevent an abnormal condition of the network system from occurring, or restore the network system from an abnormal condition, the master is required to always monitor the network system for an abnormal condition.
When an abnormality is developed in one of the slave apparatuses, for example, the state report sent from the slave apparatus fails to coincide with the system state which is managed by the master. Therefore, the master resends the operation request command to the slave apparatuses, or requests the abnormal slave apparatus to stop the operation. Consequently, a large burden is imposed on the master.